1. Field of the Invention
The invention relates to a digital data recording and reproducing apparatus and digital data reproducing apparatus for recording digital data that is supplied continuously in the time axis and includes many noises to a magnetic tape and reproducing the digital data from the magnetic tape.
2. Description of the Related Art
There has been known a magnetic tape recording and reproducing apparatus (hereinafter, referred to as a data recorder) including as one element a driving apparatus in which a cassette tape on which digital data is recorded can be loaded and being connected to a host computer via an interface, so that the driving apparatus is used as an external storing device of computer. One of the data recorders, a data recorder of a helical scan type for recording digital data onto a cassette tape by rotary heads has been known.
Such a data recorder is connected to a host computer via an interface unit by an interface of, for example, the SCSI (Small Computer System Interface) standard. Since the interface unit is recognized as a data recorder by the host computer, it has a function (called a formatter) for making file format onto the tape and performing a transmission and a reception of the data thereon. A buffer memory to temporarily hold data that is transferred between the host computer and the data recorder is provided in the interface unit.
When signal processes such as recording and reproduction of data are performed and errors which cannot be corrected (uncorrected error) are generated, by using the data temporarily stored in the buffer memory, a re-recording/re-reproduction (write retry/read retry) can be performed to the magnetic tape. As such a method, for example, when the data is read out from the buffer memory and is recorded onto the tape on a buffer unit basis, the write retry is performed in a portion (including a unrecorded area) that has been progressed from an area which could not be recorded toward an end direction of the tape and corresponds to a portion other than a data area to be recorded. Upon reproduction, the read retry is performed from an area which could not be reproduced.
In such a data recorder, besides the ordinary data that is transferred between the data recorder and the computer as mentioned above, data which is obtained by an observation, a measurement, and the like is handled. For example, there are data that is transmitted from a satellite, distortion measurement data which is obtained by measuring by using an ultrasonic wave in a tunnel, and the like. Such data is called instrumental data. The instrumental data includes much noises and at the time of actual use, a large amount of data to be abandoned is generated. The instrumental data is continuously supplied to the data recorder because of a nature of the data.
In the data recorder, to certainly write data onto a magnetic tape, upon recording, the data written on the magnetic tape is read just after the recording and an error check is performed. If the data is not correctly written as a result of the error check, the write retrying process is performed as mentioned above.
However, in case of handling the instrumental data, even if a large amount of data which contains a lot of noise and is actually abandoned is generated, since each data is essential, it is necessary to write the data continuously in the time axis in association with supplying the data in the time axis. As the result, there is a problem such that the execution of the write retrying process is unpreferable.